The present invention, in some embodiments thereof, relates to methods of modulating production of phenylpropanoid compounds in plants and, more particularly, but not exclusively, to plant extracts obtained therefrom.
In nature, flower color and fragrance are among the main means adopted by plants to attract pollinators, thereby ensuring plant reproductive success. These characteristics are also commercially important, in that they greatly influence the yield and quality of crops and their commercial appeal.
Flower scent is a composite character determined by a complex mixture of low-molecular-weight volatile molecules, classified by their biosynthetic origin into terpenes, phenylpropanoids and fatty acid derivatives [Chappell, J. and Jones, R. L. (1995) Palo Alto, Calif.: Annual Reviews Inc; Croteau, R. and Karp, F. (1991) In: Perfume: Art, Science and Technology (Lamparsky, D. and Müller, M., eds), pp. 101-126. New York: Elsevier Applied Sciences; Dudareva, N., et al. (2004) Plant Physiol. 135: 1893-1902]. Several structural genes responsible for the formation of volatile compounds have been identified [Schuurink, et al. (2006) Trends Plant Sci. 11: 20-25; van Schie, et al. (2006) Curr. Opin. Plant Biol. 9: 203-208], including genes responsible for the formation of volatile phenylpropanoid and benzenoid compound [Boatright, et al. (2004) Plant Physiol. 135: 1993-2011; Dexter, et al. (2007) Plant J. 49: 265-275; Kaminaga, et al. (2006) J. Biol. Chem. 281: 23357-23366; Tieman, et al. (2006) Proc. Natl. Acad. Sci. USA, 103: 8287-8292], however the precise biochemical steps determining the pathway are still largely unknown (Boatright et al., supra; Schuurink et al., supra). A moderate increase in volatile terpenoid production has been previously achieved in flowers and fruits via ectopic expression of specific structural genes e.g. basil geraniol synthase, tobacco limonene, γ-terpinene and β-pinene synthase, clarkia linalool synthase, strawberry linalool/nerolidol symthase [Davidovich-Rikanati, et al. (2007) Nat. 25: 899-901; Lucker, et al. (2006) In: Biology of Floral Scent (Dudareva, N. and Pichersky, E., eds), pp. 321-338. Boca Raton, Fla.: CRC Press].
Engineering of floral scent is often limited by a shortage of substrate availability, which restricts metabolic flow [Lucker et al., supra; Schwab, W. (2003) Phytochemistry, 62: 837-849]. Moreover, volatile production in plants often has a rhythmic pattern, and is thus limited to a certain period of the day. For example, in Petunia axillaris, rhythmus of volatile production is nocturnal, and has been reported as both circadian and light controlled [Schuurink et al., supra; Underwood, et al. (2005) Plant Physiol. 138: 255-266; Verdonk et al. (2003) Phytochemistry, 62: 997-1008]. One way to increase floral scent production is to use transcription factors that control multiple steps in various branches of the pathway [Koes et al. (2005) Trends Plant Sci. 10: 236-242; Mahmoud and Croteau (2002) Trends Plant Sci. 7: 366-373; Pichersky and Dudareva (2007) Trends Biotechnol. 25, 105-110], for example, the transcription factor ODORANT1 which has been shown to be involved in the regulation of volatile biosynthesis in flowers, however, its ability to boost metabolic flow toward scent production remains to be investigated [Verdonk et al. (2005) Plant Cell, 17: 1612-1624].
Another class of metabolites determining showy traits is the anthocyanin pigments which are derived from a well-defined branch of the phenylpropanoid pathway. Numerous structural as well as regulatory genes involved in anthocyanin biosynthesis have been extensively used for the genetic manipulation of flower color e.g. chalcone synthase (Chs), chalcone isomerase (Chi), flavanone 3 hydroxylase (F3h), flavonoid 3′-hydroxylase (F3′h), flavonoid 3′5′-hydroxylase (F3′5′h), flavonol synthase (Fls), flavone synthase (Fns), dihydroflavonol 4-reductase (Dfr), anthocyanidin synthase (Ans), anthocyanidin 3-rutinoside acyltransferase (Ar-at), anthocyanidin 3-glucosyltransferase (3Gt), anthocyanidin 3′-glucosyltransferase (3′Gt), anthocyanidin 3-glucoside glucosyltransferase (3Ggt), anthocyanin 3-hydroxycinnamoyltransferase (3Hat), anthocyanin 3-malonyltransferase (3Mat), anthocyanidin 3-glucoside rhamnosyltransferase (3Rt), maize leaf colour (Lc) and C1, snapdragon Delila [Chandler et al. (2007) Critical Reviews in Plant Sciences, 26(4): 169-197; Winkel-Shirley (2001) Plant Physiol. 126: 485-493]. The regulation of anthocyanin biosynthesis has been shown to occur primarily through the action of Myb transcription factors (Koes et al., supra). However, the activities of some of these regulators are not restricted to the anthocyanin shunt. For example, Pap1 (Production of Anthocyanin Pigment 1) Myb transcription factor from Arabidopsis thaliana regulates the production of various non-volatile compounds via regulation of several dozens of genes belonging to the phenylpropanoid pathway [Borevitz, et al. (2000) Plant Cell 12: 2383-2393; Harmer et al. (2000) Science 290: 2110-2113; Sharma and Dixon (2005) Plant J. 44: 62-75; Tohge et al. (2005) Plant J. 42: 218-235; Xie et al. (2006) Plant J. 45: 895-907]. For example, in Arabidopsis, overexpression of Pap1 results in the accumulation of lignin, hydroxycinnamic acid esters and flavonoids including anthocyanins, which impart a prominent purple color to plant organs (Borevitz et al., supra).
U.S. Pat. No. 7,087,552 discloses methods for creating, manipulating, modifying and enhancing floral scent in plants and cut flowers by modifying the biosynthesis and/or emission of floral scent from a plant and/or plant cutting. U.S. Pat. No. 7,087,552 teaches applying to the plant or flower a composition containing a floral scent precursor such as benzoic acid, phenylalanine, trans-cinnamic acid, benzylalcohol, salicylic acid, geranyl pyrophosphate, farnesyl pyrophosphate, jasmonic acid, eugenol or isoeugenol.
U.S. Pat. No. 5,283,184 discloses methods and compositions for producing plants (e.g. Petunia and Chrysanthemum) exhibiting one or more desired phenotypic or genotypic traits (e.g. reduction in color intensity, an altered pattern color, or a change in basic color of the plant flowers or other plant organs) by introducing into the plant cell a nucleic acid fragment (e.g., a flavonoid biosynthetic pathway gene sequence) that is transcribed to yield a mRNA transcript substantially homologous to the gene's transcript.
U.S. Pat. Appl. No. 20050289662 discloses genetically modified plants comprising a reporter system capable of directly monitoring a phenotypic trait in a plant (e.g. soil pollution). The reporter system for plants according to the teachings of U.S. Pat. Appl. No. 20050289662 may comprise an altered expression (e.g. overexpression) of transcription factors containing a Myb domain such as PAP1 and/or PAP2.
U.S. Pat. Appl. No. 20040128711 discloses method and compositions for the modulation of flavanone and/or isoflavone production in plants by introducing a transgene encoding the PAP1 gene into the plant.